Method and apparatus for making apertured masks



Jan. 7, 1958 F fg. 3

R. D. EATON METHOD AND APPARATUS FOR MAKING APERTURED MASKS Filed March 23.

INVENTUR. ROLAND D. EATON BVMQVM AT TORNE YS United States Patenti O 2,819,380 METHOD AND APPARATUS FOR MAKING APERTURED MASKS Roland D. Eaton, Radbnrn, N. J., assignor to Allen B.

Du Mont Laboratories, Inc., Clifton, N. I., a corporation of Delaware Application March 23, 1953, Serial No. 343,990 Claims. (Cl. 219-69) This invention relates to color television, and particularly to a system for producing apertured plates or masks for'use in dot-pattern color television tubes.

In dot-pattern color television tubes, there is employed a phosphor screen having areas of variously colored phos phors arranged in groups, the most commonly used group of phosphors being in the form of a triad of three closelyspaced dots of phosphors, each phosphor having a different color response when struck by an electron beam. An apertured mask is placed behind and parallel to the phosphor screen, and contains apertures aligned respectively with each triad group of color dots. When an electron beam is directed toward the phosphor screen through the apertures in the mask, the beam will strike only those phosphors having a selected color, the desired color being selected by controlling the angle at which the electron beam approaches the apertured masking plate. This angle of the electron beam may be controlled either by employing three separate electron guns to produce three electron beams directed toward the aperture plate from slightly different angles, or by employing a single electron gun and magnetic means for selectively altering the position of the apparent source of the electron beam. In color television tubes such as have been described, it is imperative that the apertures in the masking plate be accurately aligned with the respective triads of color phosphor dots. Any slight deviation from true alignment of the apertures in the mask with respect to the color triads will result in improper coloring of the television picture.

An object of the present invention is to produce an improved apertured mask or plate for color television tubes, and to produce apertures in a mask accurately and in conformity with a predetermined pattern. Other objects will be apparent.

The invention comprises, essentially, a system and apparatus for melting holes, in a mask, with an electron beam.

Referring to the drawing, Figure l shows a system and apparatus for carrying out the invention,

Figure 2 shows a mask structure suitable for use with the invention, and

Figure 3 is a sectional view taken on the line 3 3 of Figure l, and shows an aperture made in the mask in accordance with the invention.

The embodiment of the invention shown in Figure 1 comprises an evacuated television picture tube envelope 11 containing a phosphor screen 12 having thereon groups or triads 13, 14, l5, 16 of dots of dilerent color-producing phosphors, a masking plate 21 in which it is desired to form apertures in positions corresponding respectively with the positions of the color dot triads 13 16, and an electron gun 22 preferably comprising a cathode 23, a control grid 24, and an accelerating or focusing anode 26. The electron gun 22 produces an electron beam 27 which is directed toward the mask 21 and phosphor screen l2. A color control coil 31 is positioned outside the envelope 11 so as to selectively deflect or distort the electron beam 27 in order to produce a virtual source 32 of the electron beam 27, this virtual source of the electron beam being capable of being changed by the electric field of the coil 31 so as to cause the electron beam to approach the mask 21 and screen l2 from predetermined differing angles, as is well known in the art.

Suitable deflection coils 30 are provided external to the envelope 11 to produce suitable horizontal and vertical scansion of the electron beam 27, in the well known manner. A source 36 of voltage renders the grid 24 relatively negative in polarity with respect to the cathode 23. Another source 37 of voltage renders the accelerating anode 26 relatively positive in polarity, and another source 38 of voltage renders the mask 21 still further positive in polarity.

Positioned in front of the phosphor screen 12 is a filter plate 41 which passes light of one of the colors employed in the color dot triads on the screen 12. A photo-tube 42 is positioned in front of the filter 41 so as to pick up the light from the screen 12 of any one desired color as determined by the filter 41. A cathode terminal 43 of the photo-tube 42 is connected to a source 44 of negative voltage, the remaining terminal thereof being grounded as shown. An anode connection 46 of the photo-tube 42 is connected through a load resistance 47 to ground, and through a coupling condenser 48 to a control electrode 49 of tube 51 contained in a feedback amplifier 52. The control electrode 49 is returned to electrical ground through a resistor 53. A cathode 54 is electrically grounded through a bias resistor 56. An anode or output electrode 57 is connected through a load resistance 58 to a source 59 of operating voltage. The anode 57 is connected through a coupling condenser 61 to the control electrode 24 in the television tube 11.

In the preferred structure of the mask 21, shown in Figure 2, there is provided a screen 66 or mesh-like structure on which is deposited or attached a temporary layer of collodion or lacquer material 67, then a layer of beryllium 68, and then a layer of aluminum 69. The collodion lm 67 acts as a temporary barrier coating, and is baked out and removed before the masking screen is used. The mask may be prepared as follows. A film of collodion material 67 is formed on the surface of water or other suitable liquid. The mesh 66 is then raised through and out of the liquid, whereby the collodion film 67 becomes attached thereto. The beryllium and aluminum coatings 68, 69 are then successively evaporated onto the barrier coating 67, whereupon the unit is baked, whereby the barrier coating 67 is driven off, leaving the metallic coatings 68, 69 on the mesh material 66 in the finished mask blank 2l.

The mask blank 21 is then positioned in the envelope 11 as shown in Figure l. The color control coil 31 is adjusted to produce the proper virtual beam source 32 corresponding to the color of the filter 41. The deflection coils 30 are then actuated, in the normal manner, to scan the beam 27 across the mask blank 21 and phosphor screen 12. The electron beam 27 is, at this point, adjusted to an intensity sufiicient to penetrate the mask blank 21 and produce light by striking the phosphors on the screen 12. As the beam 27 is thus being scanned over the screen 12, wherever the beam hits a phosphor dot 71 which produces light of a color corresponding to that of the `filter 4l, this light is picked up by the photo-tube 42 thereby producing an electrical impulse which is fed through the amplifier 52 to the control electrode 24 of the electron gun 22 in such a polarity as to intensify the electron beam 27 to a value which causes the beam 27 to burn or melt an aperture opening 72 in the mask 2l. This opening 72 will be positioned in a position exactly corresponding to the location of the beam 27 in passing through the mask 21 to atasco strike squarely the phosphor dot 71. If the virtual source 32 of the beam 27 is properly located, the aperture 72 will be positioned symmetrically with respect to the three phosphor dots forming the triad 14. Similarly, when the beam 27 scans the screen 12, other apertures will be burned or melted into the mask 21 in positions corresponding exactly to the positions of the various triad phosphor patterns on the phosphor screen l2.

It will be appreciated that, in accordance with the invention, apertures are formed in the mask 21 in exactly corresponding positions to the positions of the color dot triads on the viewing screen 12. The process is done quickly and automatically due to the novel structure including the intensifier feedback amplifier 52. The electron beam intensity required for sufn`cient penetration through the mask blank 21 to excite the phosphor dots preferably is greater than the normal beam intensity ernployed in operation of the color television tube. The beam intensity required for burning or melting the openings 72 through the mask 21 is greater than that required for penetration through the mask to cause actuation of the photo-tube 42 in the aperture-forming process.

Figure 3 shows the appearance of the aperture 72 formed in thc mask 21 by the electron beam 27. The edges of the openings 72 form rounded surfaces 76 due to the melting action which accompanies the aperturemaking process. The thickness of the materials forming the mask blank 21 is such that the electron beam 27 will burn or melt holes 72 therein when intensified as has been described.

After the apertures 72 have been formed in the mask 21 as described. the tube 11 is ready for operation. Alternatively, the envelope 11 may be an evacuating or pumping system in which successive aperture masks 21 are formed corresponding to triad color screens 12, these screens and masks then being removed and positioned in television viewing tubes. Or, a single screen 12 may be used for making several apertured masks 21.

The aperture-burning process can be carried out with only a single color filter 41 as has been described above. The process need not be repeated with different color filters, since the apertures 72 are properly formed by the one-step scanning and beam intensifying process as has been described.

While a preferred embodiment of the invention has been shown and described, various modifications thereof will occur to those skilled in the art which will fall within the scope of invention as defined in the following claims.

What is claimed is:

1. Apparatus for forming apertures in a mask plate,

comprising a phosphor screen having areas thereon of a phosphor which emits light when impinged upon by an electron beam, a source of an electron beam directed toward said phosphor screen, said mask plate being in the path of said electron beam, means for scanning said electron beam, said beam having sufficient intensity to penetrate said mask plate and impinge upon said phosphor screen, and means to intensify said beam sutiiciently to melt a hole through said mask whenever said beam impinges upon one of said areas of phosphor.

2. The apparatus in accordance with claim 1, in which said means to intensify said beam comprises a phototube device positioned to be energized by light from said phosphor areas, and means to intensify said electron beam when said phototube device is energized.

3. Apparatus for forming apertures in a mask plate in accordance with a pattern of phosphor areas on a phosphor screen, comprising a source of an electron beam directed toward said phosphor screen through said mask plate, and means for temporarily intensifying said electron beam to melt holes in said mask plate whenever said beam strikes said phosphor areas. y

4. An electron permeable mask plate comprising a support screen, a layer of beryllium on said screen, and a layer of aluminum on said beryllium layer.

5. Apparatus for cathode ray tubes comprising a phosphor screen having phosphor areas thereon which emit light when impinged upon by an electron beam, means for generating and directing an electron beam toward said screen, an electron permeable masking plate in the path of said beam, said plate comprising a supporting screen, a layer of beryllium thereon and a layer of aluminum on said beryllium, means for scanning said electron beam and means to vary the intensity of said beam sufficiently to penetrate and provide openings in said mask in beam alignment with respect to said phosphor areas said means comprising a phototube device positioned to be energized by light from said phosphor areas.

References Cited in the file of this patent UNITED STATES PATENTS 1,594,061 Jones July 27, 1926 2,261,154 Hansen Nov. 4, 1941 2,267,714 Borries Dec. 30, 1941 2,267,752 Ruska Dec. 30, 1941 2,345,080 Ardenne Mar. 28, 1944 2,515,267 Salisbury July 18, 1950 2,549,596 Hamilton Apr. 17, 1951 2,565,768 Gittings Aug. 28, 1951 

